This invention relates generally to thermal insulation, and more specifically to fibrous blanket duct insulation or other forms and applications of insulation with vapor-barrier jackets.
Fibrous blankets, also known as duct wrap, with vapor-barrier/finish jackets are one of the most widely used materials in the insulation of heating, air conditioning, and other conduits in buildings and industry. Standard fibrous blankets are packaged in rolls of 50 foot, 75 foot, or 100 foot lengths. The insulation width is typically 48 inches, and the jacket width is 50 inches, which includes the 2-inch wide jacket attachment-flange. Other widths or lengths may be available. The insulation is available in various thickness and densities. It is faced with a laminated jacket of foil, fiberglass strand reinforcement, and kraft paper or other membranes or films, and the jacket has a continuous two-inch attachment-flange that extends two inches beyond the insulation material. The rolls of insulation are compression rolled and bound with strips of material adhered around the roll. The rolls are placed in plastic bags with the bag closed by binders. The two-inch jacket attachment-flange that extends from the edge of the insulation may become crumpled or pressed down in contact with the end of the roll of insulation.
A common procedure for installing insulation includes the insulation being transported to a job site in rolls where it is cut to length, piece by piece, as it is installed. Each roll of material is equipped with one two-inch wide jacket attachment flange along the longitudinal length of the roll. One workman rolls out the material and makes cuts of the material on the floor near where the system to be insulated is located. The workman usually gets in a kneeling position, or down on hands and knees, as it is otherwise difficult to reach completely across the 4-foot width. Measurement is made for the length to be cut on both edges of the material after it is unrolled onto the floor, and a straight edge is placed on the marks, and the cut is made with a knife. The straight edge is moved in two inches from the end and another cut is made through insulation material, being careful to cut only through the insulation but not through the jacketing. The fibrous insulation is then pulled from the jacket on the two-inch width piece leaving a jacketing attachment-flange without insulation. Each piece now has one factory or shop-provided two-inch wide jacket attachment flange and one field cut two-inch wide jacket attachment flange.
The workman next gets up from the floor and deliver the cut piece to the installing workman. This is repeated for each piece required. This job-site cutting method is very time consuming and strenuous, subjecting the workman to the possibility of strains and sprains as well as exposing the workmen and other job site personnel to airborne fibers. These fibers may be both an epidermal irritant and a respiratory hazard. On some larger construction projects, such as hospitals, the insulation of ductwork may take many months to complete.
The applicator places the cut piece around the duct, and the opposite longitudinal ends are pulled together, overlapping the flange from one end over the opposite end. The orientation of the piece during application results in the factory or shop jacket attachment flange being in an installed circumferential position in relation to the duct, and the cut end jacket attachment-flange being installed in a longitudinal position in relation to the duct. The flange is then stapled to the jacket of the opposite end with a flare-type staple.
Failure of the flare-door-type staple guns is common, and since many job sites are in remote locations, the failure of the staple gun delays work and increases costs. Stapling provides mechanical attachment, and the insulation is actually held in place on the duct by the staples and by any adhesive bonding provided by the tape.
Typically, for rectangular or square ducts having a width of over 24 inches, insulation anchors may be installed prior to installing the insulation. The anchors may be installed on the surface of the bottom of the duct or as required to hold the insulation tight to the surface. These anchors are load bearing and prevent the insulation sagging down from the bottom of the duct.
When pieces are being installed on large duct, two applicators may be required, one to hold the first end of the piece in place on the duct and the other to wrap the material around the duct and to attach the overlapped ends with staples. The two-inch jacket attachment-flange on one side of the circumferential length of the installed piece may require straightening or smoothing and may be even folded under the insulation. As successive pieces are installed, after the two-inch jacket attachment-flange on the circumferential length is straightened and smoothed, it is overlapped onto the adjacent installed piece and is stapled in place.
After stapling is completed, the applicator cuts pieces of pressure sensitive tape with release strip from a tape roll. The tape is of similar type as the insulation jacket material. The applicator next peels a section of the release strip from the end of the cut piece of tape. Many times starting the peel of the release strip can be difficult and take time. The applicator next adheres the end of the cut piece of tape over the insulation jacket attachment flange edge. The remaining release strip is removed as the length of the tape is applied over the length of the staples and flange edge. The tape is then rubbed with a squeegee or other smooth object to insure complete seal of all joints.
Cutting and applying tape takes considerable time, as access may be difficult and require stooping and reaching, as most applications are accomplished from ladders or scaffolds. Also, removal and management of release strips takes time. Care must be taken to make sure that every joint both circumferential and longitudinal is sealed completely.
If the joints are not completely sealed on the insulation jacketing installed on duct (such as air conditioning duct, which operates at a temperature lower than ambient temperature), moisture may enter the insulation, making the insulation wet and ineffective. This results in condensation drips that damage ceilings and interiors of buildings. Molds may result from this wet insulation and wet surfaces, resulting in damage and an indoor air pollution problem.
The technique for installing insulation on heating, air-conditioning, and ventilation ductwork and other fluid conduit has changed minimally over the last 30 to 40 years. Prior to that time, suitable pressure-sensitive tape was not available, and a liquid adhesive was brush applied under the overlap jacket flanges or a mastic coating, with or without reinforcement, was used over all joints to achieve a seal.
Attachment tabs are commonly used on several types of insulation covers today. They are usually fabric or rope type tabs or straps and are common on fabric encased removable and reusable pipe valve, flange and fitting covers. Many are equipped with Velcro fasteners.